My winter Force project

[Bigprairie1]

Well here it is the upcoming winter project. The motor is a '91/90hp Force with a cracked/split lower unit. I hope to either fix the bottom end of this motor...or I'll simply keep the prop as a spare and perhaps test/use the tilt-trim unit. Otherwise if complete dis-interest or boredom sets in then perhaps I'll part it out if its not retrievable.
1st thing will be a compression test to ensure that is a good starter candidate as a spare.
Now...whats driving this particular project choice?....well 90% curiousity I guess. Plus my existing motor is '90/90hp motor.
Wish me luck....oh and ideally any good advice.
ps: Frank...this is the lower unit I queried you about in a previous thread....and I may not be done yet.

 

[Frank Acampora]

Re: My winter Force project

That photo of the cracked lower unit is why the factory recommends removing the spool once a year. Aluminum corrosion is about ten times the volume of mass aluminum. As the spool corrodes, it expands, cracking the lower unit gearcase. The prevention: Remove and clean the spool before it gets corroded badly enough to crack the case. Replace the two O ring seals.

Difficult to tell from the photo but it looks like the lower unit has water intakes on the gearcase leg above the torpedo. If this is so, that is a dual exhaust unit with exhaust exiting through the prop hub AND exhaust snout.

Single exhaust lower units should fit but you may lose a little performance--I don't know, never ran a dual exhaust gearcase. I have vented the gearcase above the cav plate (not strictly legal) and this mod does increase power some because of less back pressure. Makes a lot more noise though.

 

[baxtr]

Re: My winter Force project

That photo of the cracked lower unit is why the factory recommends removing the spool once a year. Aluminum corrosion is about ten times the volume of mass aluminum. As the spool corrodes, it expands, cracking the lower unit gearcase. The prevention: Remove and clean the spool before it gets corroded badly enough to crack the case. Replace the two O ring seals.

.

Care to ellaborate on cleaning out the "spool" Frank? I have never heard of that one and I am a bit curious about it.

thanks,
Brian

 

[Frank Acampora]

Re: My winter Force project

The anode behind the prop screws into the spool. It is called the spool because it it shaped roughly like an empty thread spool. It carries the prop shaft, prop shaft seal and a needle bearing for the shaft. To remove it, you first drain the lower unit, remove the anode, and remove the four bolts and O ring seals under the bolts that hold it in. Then using all-thread screwed into the anode screw holes, fabricate a puller to remove the spool. Clean it off, clean the case areas where the O rings on each end of the spool seal, and replace O rings with new ones. (smaller end of the spool seals oil in the gearcase, larger outer end seals water pick-up for pump) Check and/or replace the prop shaft seal at this time also. Coat O ring areas on spool and case with lots of anti-seize and reassemble. Corroded ones can be a ***** to get out and you may strip the anode screw holes. If so, re-tap them from 1/4 to 5/16 size. No need to drill--stripped 1/4 are nearly the correct size to tap 5/16.

The spool also holds the thick aluminum disc that carries the reverse gear and bearings in the correct spot in the gearcase. Sandwiched in between them are two half circle rings that locate the whole assembly and keep reverse gear properly aligned with the pinion.

Obviously, since you need to drain the lower unit oil, this is best done when you change the oil for the year.

Now, these instructions are for the single exhaust unit. Dual exhaust may be different but probably fairly similar. eg. I don't think there is an anode behind the prop on dual exhaust units, and the spool shape may be different because of the necessity of passing exhaust.

 

[QuadManiac]

Re: My winter Force project

And for future reference, Frank, how do we determine whether ours is single or dual exhaust? I too have a '91 90hp.

 

[baxtr]

Re: My winter Force project

I think that the single exhaust has the water intake screens inline with the prop, on the "bullet" section that is cracked on yours

 

[baxtr]

Re: My winter Force project

I think that the single exhaust has the water intake screens inline with the prop, on the "bullet" section that is cracked on yours

 

[Frank Acampora]

Re: My winter Force project

Single exhaust has the water intakes on either side of the torpedo just behind the prop.
Dual exhaust has a series of holes vertically above the torpedo running almost to the cav plate about midway back on the leg.

I don't think dual exhaust is too common. I have only seen one Force with it.

 

[Bigprairie1]

Re: My winter Force project

This dual exhaust/single exhaust thing is pretty interesting. Both of the motors I have use this design (again one is a '90 the other a '91).
This is an important point because some of the lower units I have seen for sale on ebay have/had a different looking intake system then the ones on mine. They must have the single exhaust type/style. As a result I wasn't sure as to buy one of these styles types.
Would a single exhaust type fit my current dual exhaust motor?...or should I try to stay with the style I have, which would be the safer thing to do I suppose.
As well, is there any known difference to performance or cooling efficiency between the single/dual exhaust style?
....interesting stuff all around. I look forward to pulling that unit off. As I work through elements and issues on this motor I will be happy to post as many photos as possible if it helps anyone understand their motor further. As well, if you need references off of this motor for something just let me know.

 

[QuadManiac]

Re: My winter Force project

So, which is this, single or dual? (I'm guessing single from the statements so far) This is my 1991 90hp.

 

[QuadManiac]

Re: My winter Force project

Double post, sorry.

 

[QuadManiac]

Re: My winter Force project

Okay.... THIS must be the single (pic from eBay) and mine (above) is a dual, right?

In a single, where does the exhaust exit, snout or prop?

 

[Bigprairie1]

Re: My winter Force project

Quad...I think you have it right the second time. The white lower unit shown (from Ebay) is a single and yours is a double...which I think is identical to the motor(s) I have.
I have noticed that one of the differences however between the '90 and the '91 I have is in the coils and that power pack arrangement. My mtd/working '90 has a blue set (Prestolite...I think) while the '91 looks quite different with black coils and a slightly different looking electrical power arrangement.
However my starting point is going to be to source a new lower unit (housing? or complete?). From there will come the rebuild/re-assembly.
Providing and contingent on the compression test showing a reasonably healthy result.
Frank...any comments on those two lower units Quad posted?...are they interchangeable to your knowledge?

 

[QuadManiac]

Re: My winter Force project

BigP, according to my manual, the 1990A version uses Prestolite ignition, the 1990B thru 1996 uses the Thunderbolt ignition system, so it sounds like your assessment is correct.

BTW, also according to my manual, the displacement increased slightly between the '90A and those after, from 72.4 ci to 75.2 ci through an increase in bore from 3.312 inches to 3.375 inches... so some parts (pistons are the first that come to mind) will not be interchangeable between the two models.

Question, again, where does the exhaust exit in a single exhaust unit, snout or prop?

 

[baxtr]

Re: My winter Force project

snout